1. Field of the Invention
The present invention relates to a liquid crystal display device, and particularly, to a 2-dot inversion liquid crystal display device that prevents cross talk and occurrence of a dim phenomenon along a transverse direction.
2. Description of the Background Art
Generally, a liquid crystal display (LCD) device is a transmissive type flat panel display device having a wide application to various electric devices, such as mobile phones, personal digital assistants (PDA), and notebook computers. The LCD device can be used as a small, light, and power-efficient device for superior image quality. Accordingly, the LCD device has practical application in digital television displays. In addition, the LCD device can be categorized according to the method it uses for moving liquid crystal molecules. However, an active matrix thin film transistor (TFT) LCD is commonly used due to its rapid reaction speed and low residual image generation.
FIG. 1 is a plan view of a liquid crystal display device according to the prior art. In FIG. 1, a TFT LCD panel 1 structure includes a plurality of gate lines 3 and data lines 5 arranged along longitudinal and transverse directions for defining a plurality of pixel regions, a thin film transistor (TFT) 7, which functions as a switching device, is disposed in each of the respective pixel regions, and a storage capacitor 11 electrically interconnected between the TFT 7 and a pixel electrode 9. The TFT 7 is switched when a scan signal is input via a corresponding one of the gate lines 3 to transmit the signal input through the data line 5 to the pixel electrode 9. Accordingly, an electric field is applied to a corresponding liquid crystal material by the pixel electrode 9 and a common electrode (not shown).
FIG. 2 is a cross-sectional of a pixel in the liquid crystal display device shown in FIG. 1 according to the prior art. In FIG. 2, a metal gate electrode 22 is formed on a transparent lower substrate 20, and a gate insulating layer 24 is formed on an entire surface of the lower substrate 20 upon which the gate electrode 22 is formed. A semiconductor layer 26 is formed on the gate insulating layer 24, and metal source/drain electrodes 28 are formed thereupon. In addition, a transparent metal pixel electrode 30, such as indium tin oxide (ITO), is formed upon the gate insulating layer 24 and is electrically connected to the source/drain electrode 28, and a passivation layer 32 is formed on the pixel electrode 30.
In FIG. 2, a black matrix 42, which functions as a light shielding layer to prevent deterioration of image quality by light leakage, is formed on an upper substrate 40 corresponding to a region of the gate electrode 22, and a color filter layer 44 is formed on an image representation region corresponding to the pixel electrode 30. A transparent metal common electrode 46 is formed on the black matrix 42 and on the color filter layer 44. A constant cell gap is maintained between the lower and upper substrates 20 and 40 by a spacer 52. Accordingly, the liquid crystal material is injected between the upper and lower substrates 40 and 20 to form a liquid crystal material layer 50. Although not shown in FIG. 2, alignment layers for aligning liquid crystal molecules of the liquid crystal material layer 50 are formed on the passivation layer 32 of the lower substrate 20 and on the common electrode 46 of the upper substrate 40.
In FIG. 2, a channel layer is formed in the semiconductor layer 26 by application of the scan signal on the gate electrode 22, whereby the data signal input from the data line 5 through the source/drain electrodes 28 is applied to the liquid crystal material layer 50. On the other hand, as shown in FIG. 1, each gate electrode 22 of the TFT 7 is electrically interconnected to the gate line 3. Accordingly, as the scan signal is applied to the gate line 3, channel layers of each of the semiconductor layers of each of the plurality of TFT 7 connected to the corresponding gate line 3 are formed, whereby transmitting the data signal input through the data line 5 to each of the corresponding pixel electrodes 9.
Methods of operating the liquid crystal panel 1 (in FIG. 1) may be divided into one of a line inversion method, a column inversion method, or a dot inversion method according to the phase of the data signal applied to the data line 5. The line inversion method applies the data signal to each of the data lines after inverting the phase of the data signal per each of the data lines, and the column inversion method sequentially applies the data signal to each of the data lines after inverting the phase of the data signal per each column. In addition, the dot inversion method simultaneously inverts the voltage polarity applied to the data line 5 on every column and every line. Due to deterioration of the liquid crystal material when the same voltage is continuously applied between the pixel electrode and the common electrode, the phase of the data signal is inverted and the data signal is applied to the data line 5 in order to prevent a cross-talk phenomenon on the display screen when the liquid crystal display device is fabricated.
FIGS. 3A and 3B show driving methods of an odd frame and an even frame in a liquid crystal display device of dot inversion method according to the prior art. In the dot inversion method, the amount of cross-talk is relatively less in the dot inversion method than cross-talk in the line inversion method or in the column inversion method. Accordingly, the dot inversion method produces a higher image quality. In FIGS. 3A and 3B, when a positive (+) pixel voltage is applied to an (m,n) pixel in an odd frame, a negative (−) pixel voltage is applied to an adjacent (m, n+1) pixel. In addition, when the negative (−) pixel voltage is applied to the (m,n) pixel in an even frame, the positive (+) pixel voltage is applied to an (m,n+1) pixel. In a case where a voltage decrease occurs in the positive pixel electrode of the (m,n) pixel during a predetermined period (i.e., an odd frame), the negative pixel voltage is applied to the (m,n) pixel at a next even frame. Accordingly, the voltage decrease may be compensated.
FIG. 4 shows a panel structure of a liquid crystal display device using the dot inversion method according to the prior art. In FIG. 4, in order to operate the liquid crystal display device using the dot inversion method, a first data driving integrated circuit (IC) 62 and a second data driving IC 64 are provided for dividing a data driving IC for applying the data signal to the data line 5. The data lines of odd rows are connected to the first data driving IC 62, and the data lines of even rows are connected to the second data driving IC 64. Accordingly, the scan signal is applied to the respective TFT 7 through a gate driving IC 60, whereby the pixel voltages of different phases are applied to adjacent pixel electrodes.
FIG. 5 is a signal waveform of a liquid crystal display device of dot inversion method according to the prior art. In FIG. 5, as the scan signal is input to an n-th gate line 3 through the gate driving IC 60 (in FIG. 4), a channel region is formed in the semiconductor layer of the TFT 7 (in FIG. 4) to supply a data signal of one of the first data driving IC 62 and the second date driving IC 64 to a corresponding pixel electrode via a source/drain electrode of the TFT 7. Accordingly, a positive pixel voltage and a negative pixel voltage are applied to adjacent the pixel electrodes (i.e., (m,n) pixel and (m,n+1) pixel).
In FIG. 5, ΔVp is a feedthrough voltage, which is a voltage lowering value of the pixel voltage caused by a parasitic capacitance generated between the gate electrode and the source/drain electrode, and by the parasitic capacitance generated between the data line 5 and the pixel electrode. In addition, ΔVpp is a voltage variation value caused by a coupling capacitance generated between the adjacent pixel electrodes. During the dot inversion method, the positive pixel voltage is applied to the (m,n) pixel in the odd frame, and the negative pixel voltage is applied to the (m,n) pixel in the even frame. In addition, the negative pixel voltage is applied to the (m,n+1) pixel that is adjacent to the (m,n) pixel in the odd frame, and the positive pixel voltage is applied to the (m,n+1) pixel in the even frame. Therefore, since the (m,n) pixel to which the positive pixel voltage is applied in the odd frame is adjacent to the (m,n+1) pixel to which the negative pixel voltage is applied in the odd frame, the effective voltage of the (m,n) pixel is lowered by the dislocation of the adjacent pixel (m,n+1) by a value of ΔVpp. However, the effective voltage of the pixel (m,n+1) is correspondingly increased by the value of ΔVpp by the dislocation of the adjacent (m,n) pixel. Accordingly, the (m,n) pixel and the (m,n+1) pixel are conversely operated when the odd frame is changed into the even frame, whereby the effective voltage of the (m,n) pixel is increased by the value of ΔVpp and the effective voltage of the (m,n+1) pixel is reduced by the value of ΔVpp.
By using the dot inversion method for driving the liquid crystal display device the effective voltages of the pixels to which the positive pixel voltage is applied are reduced as ΔVpp, and the effective voltages of the pixels to which the negative pixel voltage is applied are increased as ΔVpp. Thus, all the pixels have voltage dislocation values that are reduced at a side opposite to the applied pixel electrodes due to the coupling effect between the adjacent pixels. Accordingly, a luminance difference between the pixels is not generated and the cross-talk is not generated on the display screen. However, for low power consumption liquid crystal display devices, the phases of data signals applied to the respective pixels should be inverted in the dot inversion method described above.